COMPARATIVE STUDY ON SEISMIC ANALYSIS OF MULTISTOREY BUILDING STIFFENED WITH BRACING AND SHEAR WALL.

Transcription

1 COMPARATIVE STUDY ON SEISMIC ANALYSIS OF MULTISTOREY BUILDING STIFFENED WITH BRACING AND SHEAR WALL. Mohd Atif 1, Prof. Laxmikant Vairagade 2, Vikrant Nair 3 1P.G. Student, Civil Engineering Department, G.H.R.A.E.T Nagpur, Maharashtra, India 2Assistant Professor, Civil Engineering Department, G.H.R.A.E.T, Nagpur, Maharashtra, India 3Structural Consultant, Techpro Consultancy, Nagpur, Maharashtra, India *** Abstract - This research work focuses on comparison of seismic analysis of G+15 building stiffened with bracings and shear wall. The performance of the building is analyzed in Zone II, Zone III, Zone IV, Zone V. The study includes understanding the main consideration factor that leads the structure to perform poorly during earthquake in order to achieve their appropriate behavior under future earthquakes. The analyzed structure is symmetrical, G+15, Ordinary RC moment-resting frame (OMRF). Modelling of the structure is done as per staad pro. V8i software. Time period of the structure in both the direction is retrieve from the software and as per IS 1893(part 1):2002 seismic analysis has undergone. The Lateral seismic forces of RC frame is carried out using linear static method as per IS 1893(part 1) : 2002 for different earthquake zones. The scope of present work is to understand that the structures need to have suitable Earthquake resisting features to safely resist large lateral forces that are imposed on them during Earthquake. Shear walls are efficient, both in terms of construction cost and effectiveness in minimizing Earthquake damage in structure. Also the braced frames can absorb great degree of energy exerted by earthquake.. The results of the performance and the analysis of the models are then graphically represented and also in tabular form and is compared for determining the best performance of building against lateral stiffness by arrangement of three different types of bracings with three different orientation of bracings and shear wall. A comparative analysis is done in terms of Base shear, Displacement, Axial load, Moments in Y and Z direction in columns and shear forces, maximum bending moments, max Torsion in beams. Key Words: Seismic analysis, Bracings, Shear Wall, Lateral Stiffness, Indian code IS 1893:2002 and OMRF. 1. INTRODUCTION 1.1 Overview The tallness of a building is relative and cannot be defined in absolute terms either in relation to height or the number of stories. But, from a structural engineer's point of view the tall building or multi-storied building can be defined as one that, by virtue of its height, is affected by lateral forces due to wind or earthquake or both to an extent that they play an important role in the structural design. Tall structures have fascinated mankind from the beginning of civilization. The Egyptian Pyramids, one among the seven wonders of world, constructed in 2600 B.C. are among such ancient tall structures. Such structures were constructed for defense and to show pride of the population in their civilization. The growth in modern multi-storied building construction, which began in late nineteenth century, is intended largely for commercial and residential purposes. The design of tall buildings essentially involves a conceptual design, approximate analysis, preliminary design and optimization, to safely carry gravity and lateral loads. The design criteria are, strength, serviceability, stability and human comfort. Earthquakes have become a frequent event all over the world. It is very difficult to predict the intensity, location, and time of occurrence of earthquake. Structures adequately designed for usual loads like dead, live, wind etc may not be necessarily safe against earthquake loading. It is neither practical nor economically viable to design structures to remain within elastic limit during earthquake. The design approach adopted in the Indian Code IS 1893(Part I): 2002 Criteria for Earthquake Resistant Design Of Structures is to ensure that structures possess at least a minimum strength to withstand minor earthquake occurring frequently, without damage; resist moderate earthquakes without significant structural damage though some non-structural damage may occur; and aims that structures withstand major earthquake without collapse. Structures need to have suitable earthquake resistant features to safely resist large lateral forces that are imposed on them during frequent earthquakes. Ordinary structures for houses are usually built to safely carry their own weights. Low lateral loads caused by wind and therefore, perform poorly under large lateral forces caused by even moderate size earthquake. These lateral forces can produce the critical stresses in a structure, set up undesirable vibrations and, in addition, cause lateral sway of structure, which could reach a stage of discomfort to the occupants. 2015, IRJET ISO 9001:2008 Certified Journal Page 1158

2 Shear wall is one of the most commonly used lateral load resisting element in high rise building. Shear wall (SW) has high in plane stiffness and strength which can be used simultaneously to resist large horizontal load and support gravity load. The scope of present work is to study and investigate the effectiveness of RC shear wall in medium rise building. Reinforced concrete shear walls are used in Bare frame building to resist lateral force due to wind and earthquakes. They are usually provided between column lines, in stair wells, lift wells, in shafts. Shear wall provide lateral load resisting by transferring the wind or earthquake load to foundation. Besides, they impart lateral stiffness to the system and also carry gravity loads. But bare frame with shear wall still become economically unattractive. If the structural engineers consider property the non-structural element in structural design along with other elements like shear wall gives better results. The most effective and practical method of enhancing the seismic resistance is to increase the energy absorption capacity of structures by combining bracing elements in the frame. The braced frame can absorb a greater degree of energy exerted by earthquakes. Bracing members are widely used in steel structures to reduce lateral displacement and dissipate energy during strong ground motions. This concept extended to concrete frames. The various aspects such as size and shape of building, location of shear wall and bracing in building, distribution of mass, distribution of stiffness greatly affect the behaviors of structures. Bracing system improves the seismic performance of the frame by increasing its lateral stiffness and capacity. To the addition of bracing system load could be transferred out of the frame and into the braces, by passing the weak columns. The stiffness added by the bracing system is maintained almost up to the peak strength. Stiffness is particularly important at serviceability state, where deformations are limited to prevent damage. 1.2 Objective of the Project Tall building developments have been rapidly increasing worldwide. The growth of multistory building in the last several decades is seen as the part of necessity for vertical expansion for business as well as residence in major cities. It is observed that there is a need to study the structural systems for R.C.C framed structure, which resists the lateral loads due to seismic effect. Safety and minimum damage level of a structure could be the prime requirement of tall buildings. To meet these requirements, the structure should have adequate lateral strength, lateral stiffness and sufficient ductility. Among the various structural systems, shear wall frame or braced concrete frame could be a point of choice for designer. Therefore, it attracts to review and observe the behavior of these structural systems under seismic effect. Hence, it is proposed to study the dynamic behavior of reinforced concrete frame with and without shear wall and steel braced frame. The purpose of this study is to compare the seismic response of above structural systems. Axial forces and moments in members and floor displacements will be compared. The most effective and practical method of enhancing the seismic resistance is to increase the energy absorption capacity of structures by combining bracing elements in the frame. The braced frame can absorb a greater degree of energy exerted by earthquakes. The present study is an effort towards analysis of the structure during the earthquake. G+15stories residential building is considered. To analyze a multistoreyed RC framed building considering different earthquake intensities II, III, IV and V by response spectra method and find the base shear value for different structures. Seismic analysis of RC frame with bare and different position of shear wall and braced frame is carried out using Linear static analysis method as per IS 1893 (Part I): 2002[22] by using STAAD-PRO software.for this analysis different types of models are considered and comparison of seismic performance is carried out. 1.3 Methodology The methodology worked out to achieve the mentioned objectives is as follows: 1. Modeling of the selected building in Staad pro. V8i Software. 2. Retrieved time period of structure from the software. 3. Thirteen models as per the Indian code specification were prepared. Models including Bare frame, frames with shear walls and frames with bracings. 4. Applied calculated Lateral seismic forces and load combinations as per IS Analyzed the models for axial forces, moments, lateral displacements, max shear force and max torsion and graphical and tabular representation of the data is presented Time period The Equivalent static methods works on seismic coefficient, which rely on the natural time period of vibration of the structure, the earthquake resistance design of the structures requires time period to calculate the base shear. The time period of the structure has been taken from the Staad pro software. 2015, IRJET ISO 9001:2008 Certified Journal Page 1159

3 Time period in X- direction = 1.02 Sa/g = 1.33 Time period in Y- direction= 1.44 Sa/g = Load Combinations Load combinations that are to be used for Limit state Design of reinforced concrete structure are listed below. (1) 1.5(DL + LL) (2) 1.2(DL + LL ± EQ - X) (3) 1.2(DL + LL ± EQ - Y) (4) 1.5(DL ± EQ - X) (5) 1.5(DL ± EQ - Y) (6) 0.9DL ± 1.5EQ - X (7) 0.9DL ± 1.5EQ Y Distribution of the horizontal seismic forces: Load and base shear calculation has been done as per IS The base shear is calculated and distributed throughout the height at each floor of the building and the lateral seismic force induced at any level is determined. Indian standards IS-1893:2002: IS 1893:2002 is denoted as Criteria for earthquake resistant Design of structures Part 1 General provisions and buildings. The design lateral force shall first be computed for the building as a whole. Thedesign lateral force shall then be distributed to the various floor levels. This overall design seismic force thus obtained at each floor level shall then be distributed to individual lateral load resisting elements depending on the floor diaphragm action. The design base shear calculated shall be distributed along the height of the building as per the following expression: Mass and Base shear calculatons: BASE BASE ZONE MODEL TOTAL SHEAR SHEAR in TYPE MASS in X- dir Z- dir BF DB DB DB VB II VB VB XB XB XB SW SW SW BF DB DB DB VB VB III VB XB XB XB SW SW SW BF DB DB DB VB VB IV VB XB XB XB SW SW SW Mass calculations and base shear are summarized as: 2015, IRJET ISO 9001:2008 Certified Journal Page 1160

4 ZONE V MODEL TYPE TOTAL MASS BASE SHEAR in X- dir BASE SHEAR in Z- dir BF DB DB DB VB VB VB XB XB XB SW SW SW Modeling: This building has been modeled as 3D Space frame model with six degree of freedom at each node using STAAD - PRO, software for stimulation of behavior under gravity Specifications and seismic loading. The isometric 3D view and plan of the building model is shown as figure. The support condition is considered as fully fixed. The specifications used in modeling are Sr. Parameters Dimensions/Type No 1 Plan dimension 18m x 9 m 2 Number of stories G+15 3 Total height of building 48m 4 Height of each storey 3m 5 Column size 230 X 600 mm 6 Beam size 230 x 400 mm 7 Grade of concrete M20 8 Frame type OMRF 9 Soil type Medium soil 10 Live load 3 /sq.m 11 Floor finish 1 /sq.m 12 Inner wall 230 mm 13 Outer wall 230 mm 14 Slab thickness 230mm 15 Unit weights of Concrete 25 /Cum 16 Unit weights of brick 19 /Cum work 17 Shear wall thickness 200mm 18 Section for steel bracing ISA 110 X 110 X 10mm Fig-1: Plan of the selected building Fig-2: 3D View of the selected building 2015, IRJET ISO 9001:2008 Certified Journal Page 1161

5 Fig-5: Building with diagonal bracings at outer and position (DB3) inner ig-3: Buildi ng with diago nal bracin gs at corne r (DB1) F Fig-6: Building with V- bracings at corner (VB1) Fig- 4: Building with diagonal bracings at periphery (DB2) Fig-7: Building with V- bracings at periphery (VB2) 2015, IRJET ISO 9001:2008 Certified Journal Page 1162

6 Fig-8: Building with V- bracings at outer and inner position (VB3) Fig11 : Building with X- bracings at outer and inner position(xb3) Fig-9: Building with X- bracings at corner (XB1) ig-12: Building with Shear walls at corner (SW1) F Fig-10: Building with X- bracings at periphery (XB2) 2015, IRJET ISO 9001:2008 Certified Journal Page 1163

7 MAX DEFL. mm BF DB DB DB VB VB II VB XB MAX DEFL. mm XB BF XB SW1 DB SW2 DB SW3 DB VB III VB VB XB XB XB SW SW SW Fig-13: Building with Shear Walls at periphery (SW2) 2 ANALYSIS AND RESULTS 2.1 OVERVIEW A G+15 building is analyzed and compared with shear wall and three different patterns of bracings with three different positioning of it during the earthquake considering all the four zones. Parameters like displacement, axial force, bending moment for columns and shear, moment, torsion for beams are calculated. Graphical and Tabular representation of data is discussed in this chapter. 2.2 Column Maximum Displacements Table-1: Maximum lateral displacement MAX DEFL. mm BF DB DB ZONE SOIL TYPE DB3 TYPE VB1 MAX DEFL. mm BF VB V DB1 VB DB2 XB DB3 XB VB1 XB SW VB IV SW VB SW XB XB XB SW SW SW Fig13: Building with Shear walls at outer and inner pos. (SW3) Fig-2.2.1: Comparison of Maximum lateral displacement. 2015, IRJET ISO 9001:2008 Certified Journal Page 1164

8 2.2.2 Maximum Axial Force on columns Table-2: Maximum Axial Force MAX. AXIAL FORCE BF DB DB DB VB VB II VB XB XB XB SW SW SW MAX. AXIAL FORCE BF DB DB DB VB VB III VB XB XB XB SW SW SW MAX. AXIAL FORCE BF DB DB DB VB VB IV VB XB XB XB SW SW SW MAX. AXIAL FORCE BF DB DB DB VB VB V VB XB XB XB SW SW SW Fig-2.2.2: Comparison of Maximum Axial force 2015, IRJET ISO 9001:2008 Certified Journal Page 1165

9 2.2.3 Maximum Moment in columns Table-3: Maximum Moment in columns II III BF DB DB DB VB VB VB XB XB XB SW SW SW BF DB DB DB VB VB VB XB XB XB SW SW SW MAX.MOMENT m MAX.MOMENT m MAX.MOMENT m BF DB DB DB VB VB IV VB XB XB XB SW SW SW MAX.MOMENT m BF DB DB DB VB VB V VB XB XB XB SW SW SW , IRJET ISO 9001:2008 Certified Journal Page 1166

10 Fig-2.2.3: Comparison of Maximum moments(-m) Maximum Torsion in beams Table-4: Maximum Torsion in beams MAX. Torsion -M II BF DB DB DB VB VB VB XB XB XB SW SW SW MAX. Torsion -M III BF DB DB DB VB VB VB XB XB XB SW SW SW MAX. Torsion -M IV BF DB DB DB VB VB VB XB XB XB SW SW SW MAX. Torsion -M BF DB DB DB VB VB V VB XB XB XB SW SW SW , IRJET ISO 9001:2008 Certified Journal Page 1167

11 Fig-2.2.4: Comparison of Maximum Torsion in -M Maximum Shear Force in beams Table5: Maximum Shear Force in beams II III MAX. Shear Force BF DB DB DB VB VB VB XB XB XB SW SW SW BF DB DB DB VB VB VB XB XB XB SW SW SW MAX. Shear Force IV BF DB DB DB VB VB VB XB XB XB SW SW SW MAX. Shear Force MAX. Shear Force BF DB DB DB VB VB V VB XB XB XB SW SW SW Fig-2.2.5: Comparison of Maximum Shear Force in 2015, IRJET ISO 9001:2008 Certified Journal Page 1168

12 2.2.6 Maximum Banding Moments in beams Table-6: Maximum Bending Moments in beams MAX.Bending Moment (-M) BF DB DB DB VB VB II VB XB XB XB SW SW SW MAX.Bending Moment (-M) BF DB DB DB VB VB III VB XB XB XB SW SW SW MAX.Bending Moment (-M) BF DB DB DB VB VB IV VB XB XB XB SW SW SW MAX.Bending Moment (-M) BF DB DB DB VB VB V VB XB XB XB SW SW SW Fig-2.2.6: Comparison of Max Bending Moment in M 2015, IRJET ISO 9001:2008 Certified Journal Page 1169

13 CONCLUSIONS 1. Shear wall elements are very much efficient in reducing lateral displacement of frame as drift and horizontal deflection induced in shear wall frame are much less than that induced in braced frame and plane frame. 2. The location of shear-wall and brace member has significant effect on the seismic response than the plane frame. 3. The location of shear-wall- 3 is favorable as they are effective in reducing actions induced in frame with less horizontal deflection and drift. % REDUCTION OF MAXIMUML LATERAL DSLACEMENT in mm ZONE BF SW3 % Reduction ZONE-II % ZONE- III % ZONE- IV % ZONE-V % 4. Shear wall construction will provide large stiffness to the building by reducing the damage to the structure. 5. The concept of using steel bracing is one of the advantageous concepts which can be used to strengthen or retrofit the existing structures. 6. Steel bracings can be used as an alternative to the other strengthening or retrofitting techniques available as the total weight on the existing building will not change significantly. 7. Steel bracings reduce flexure and shear demands on beams and columns and transfer the lateral loads through axial load mechanism. 8. The lateral displacements of the building studied are reduced by the use of X type of bracing systems. 9. The building frames with X bracing system will have minimum possible bending moments in comparison to other types of bracing systems. 10. Using steel bracings the total weight on the existing building will not change significantly. 11. The lateral displacement of the building is reduced by 35% to 45 % by the use of X Type steel bracing system, and X bracing type reduced maximum displacement. REFERENCES [1] Himalee Rahangadle, S. R. Satone, Design and Analysis of Multistoried Building with Effect of Shear wall, International journal of Engineering Reserch and Applications, Vol 3, Issue 3, pp , ISSN: [2] Arlekar J. N., Jain S. K. and Murty C. V.R., Seismic Response of RC Frame Building with Soft First Storey, proceeding of CBRI Golden Jubliee Conference on Natural Hazards in Urban Habitat, 1997, New Delhi, pp [3] Anand. N., Mightraj. C., Prince Arulraj G., Seismic Behaviour of RCC shear wall Under Different Soil Conditions, Indian Geotechnical Conference-2012, GEO trendz, IGS Mumbai chapter ant IIT Bombay. [4] FEMA 356, Presented and Commentry for the Seismic Rehabilitation of Buildings, Federal Emergency Management Agency, Washington, [5] Nabin Raj C., S. Elavenil, Analytical Study on Seismic Performance of Hybrid (Dual) Structural System Subjected to Earthquake, International Journal of Modern Engineering Research. Vol.2, Issue.4, 2012, pp , ISSN: [6] Kumar, S. R. and kumar, G. R., Seismic Retrofit of Soft Storey Building using Steel Bracing, Workshop on retrofitting of structures, Oct 10-11, 2003, IIT Roorkee,pp [7] Lawson R.S.. Vicki Vance, Krawinkler H., Nonlinear Static Pushover Analysis- Why, When, and How?, Fifth US National Conference on Earthquake Engineering Proceeding, Vol.1, 1994, pp [8] Krawinkler H., Seneviratna G., Pros and Cones of Pushover analysis of seismic performance Evaluation, Engineering Structures, Vol.20, No.4-6,1997. [9] M.D. Kevadkar, P. B. Kodag, Lateral Load analysis of R.C.C Building, International Journal of Modern Engineering Research Vol.3, Issue3,2013. Pp , ISSN: [10] Kadid A. and Boumrkik A., Pushover Analysis of Reinforced Concrete Frames Structures, Asian Journal of Civil Engineering (Building and Housing), VOL.9, No.1, 2008,pp [11] Kabeyasawa, T., Sanada, Y. and Kuramoto, H., Design and Analysis of a Six Storey RC Frame- wall System with Soft First Storey for Shaking Table Test, Vol.35, NO.11, 2006, PP [12] Sundar M. Deshmukh, J. G. Kulkarni, Analysis of Partially Braced Multistorey Building Frames Subjected to Gravity and Earthquake Loads, International Journal of Advance Research In Science and Engineering. Vol. No.2, Issue No.8, 2013, ISSN , IRJET ISO 9001:2008 Certified Journal Page 1170